1. Field of the Invention
This invention relates to a heat-treating apparatus and a method for the same.
2. Description of the Prior Art
Heat-treating apparatus has been used for the manufacture of semiconductor devices. This manufacture includes diffusion treatment, forming of an oxide film and forming of a film by Chemical Vapor Deposition. Heat treatment by the heat-treating equipment is described in the following. A boat holding wafers subject to heat treatment is placed in the work position. The board which is holding, i.e., 50 wafers and is made of quartz is carried by an elevator to the boat delivery position of the heat-treating furnace. Then, the boat is transferred by transfer means directly from the elevator to the heat-treating furnace where the wafers are subjected to specified heat treatment.
There are various types of boat transfer means. Therefore, it is necessary to select boats and an elevator that suit the type of transfer means in order to allow the smooth transfer of boats to the transfer means.
For example, among the transfer means available on the market that bring a wafer into and out of the heat-treating furnace without the wafer being contacted by contaminants are the products called "Softlanding", "Cantilever" and "Atmoscan" made by Tel Sagami Co., Ltd.
In the "Softlanding" type, boat 10 that looks like a ship as shown in FIG. 1A is raised and carried by wafer transfer arm 12 called a fork as shown in FIG. 1B, one end of which is circular in cross section or by wafer transfer arm 12' called a fork as shown in FIG. 1C, one end of which is rectangular in cross section. As shown in FIG. 2, boat 10 holding wafers 14 is taken into heat-treating furnace 16 without physical contact with contaminants. After boat 10 is set in heat-treating furnace 16, transfer arm 12 is taken out of heat-treating furnace 16. Under this condition, wafers 14 receive heat treatment after shutting an entrance of the furnace 16.
In the "Cantilever" type transfer means, as in the "Softlanding" type, boat 10 is raised and held by transfer arm 12 or 12'. Then, wafers 14 are taken into heat-treating furnace 16 without contacting to wall of furnace 16. One difference from the "Softlanding" type is that wafers 14 are heat-treated with boat 10 still placed on transfer arm 12 or 12'.
As described above, both in the "Softlanding" and "Cantilever" transfer methods, transfer arm 12 or 12' is used to raise and carry boat 10. Hence, boat 10 is delivered at the boat delivery position as described below. Referring to FIG. 1B, there are handles 10a at the ends in the longitudinal direction of boat 10, which will be carried by an elevator. The elevator carrying boat 10 lowers in the direction indicated by the arrow mark b.sub.1 and puts boat 10 on wafer transfer arm 12. The holding of handles 10a and 10b is then released. After this, the elevator is withdrawn upward as indicated by the arrow mark b.sub.2. Thus, boat 10 has been delivered.
Meanwhile, in the "Atmoscan" transfer method, hollow, cylindrical transfer arm 18 is used as shown in FIG. 3. Transfer arm 18 is inserted into boat 10. Then, an inactive gas such as niytogen is introduced into transfer arm 18 as shown in FIGS. 4A and 4B. Wafers 14 are thereby prevented from being covered by an oxide film which is formed by reaction with oxygen in the air. Under this condition, transfer arm 18 is inserted into heat-treating furnace 16 where wafers 14 are heat-treated.
As described above, in the "Atmoscan" method, transfer ar 18 is formed in a hollow cylinder. Therefore, if boat 10 and an elevator of the same constructions as are used in the "Softlanding" and "Cantilever" methods are employed, it is impossible to deliver boat 10 into transfer arm 18 by means of the elevator. Consequently, an elevator is used which is constructed to support boat 10 from below and carry to the boat transfer position. This elevator inserts boat 10 into transfer arm 18 as it moves along longitudinal groove 18a formed in the bottom portion at the front end of transfer arm 18. When boat 10 has been delivered in transfer arm 18, the elevator goes down. Boat 10 is positioned along longitudinal slot 18a. Then, the elevator is withdrawn to the operator's side.
Incidentally, heat-treating furnaces are often installed in plural stages in heat-treating equipment. And, one elevator is used to transfer boats to the heat-treating furnaces.
In the conventional boat transfer methods, however, a certain type of heat-treating furnace must be used with a certain type of transfer means and a certain type of carrying mechanism of the elevator. As a result, a common elevator cannot be used for different types of heat-treating furnaces.
The current trend in the production of semiconductor devices is a shift from small-variety large-lot production to large-variety small-lot production. Under this situation, there has been a long felt need for the development of a heat-treating apparatus having heat-treating furnaces of different types.
However, the conventional boat transfer methods were unable to meet the above-mentioned need because boats cannot be transferred by a common elevator to different types of heat-treating furnaces.